An assessment of the state of conservation planning in Europe

Expanding and managing current habitat and species protection measures is at the heart of the European biodiversity strategy. A structured approach is needed to gain insights into such issues is systematic conservation planning, which uses techniques from decision theory to identify places and actions that contribute most effectively to policy objectives given a set of constraints. Yet culturally and historically determined European landscapes make the implementation of any conservation plans challenging, requiring an analysis of synergies and trade-offs before implementation. In this work, we review the scientific literature for evidence of previous conservation planning approaches, highlighting recent advances and success stories. We find that the conceptual characteristics of European conservation planning studies likely reduced their potential in contributing to better-informed decisions. We outline pathways towards improving the uptake of decision theory and multi-criteria conservation planning at various scales, particularly highlighting the need for (a) open data and intuitive tools, (b) the integration of biodiversity-focused conservation planning with multiple objectives, (c) accounting of dynamic ecological processes and functions, and (d) better facilitation of entry-points and co-design practices of conservation planning scenarios with stakeholders. By adopting and improving these practices, European conservation planning might become more actionable and adaptable towards implementable policy outcomes. This article is part of the theme issue ‘Ecological novelty and planetary stewardship: biodiversity dynamics in a transforming biosphere’.

Expanding and managing current habitat and species protection measures is at the heart of the European biodiversity strategy.A structured approach is needed to gain insights into such issues is systematic conservation planning, which uses techniques from decision theory to identify places and actions that contribute most effectively to policy objectives given a set of constraints.Yet culturally and historically determined European landscapes make the implementation of any conservation plans challenging, requiring an analysis of synergies and trade-offs before implementation.In this work, we review the scientific literature for evidence of previous conservation planning approaches, highlighting recent advances and success stories.We find that the conceptual characteristics of European conservation planning studies likely reduced their potential in contributing to better-informed decisions.We outline pathways towards improving the uptake of decision theory and multi-criteria conservation planning at various scales, particularly highlighting the need for (a) open data and intuitive tools, (b) the integration of biodiversity-focused conservation planning with multiple objectives, (c) accounting of dynamic ecological processes and functions, and (d) better facilitation of entry-points and co-design practices of conservation planning scenarios with stakeholders.By adopting and improving these practices, European conservation planning might become more actionable and adaptable towards implementable policy outcomes.
This article is part of the theme issue 'Ecological novelty and planetary stewardship: biodiversity dynamics in a transforming biosphere'.

Introduction
There is an urgent need to halt the decline of biodiversity in the EU, and the ecosystem services it supports.Despite important past efforts to preserve biodiversity, such as the Birds and Habitats Directives or Water Framework Directive, there has been insufficient progress towards halting biodiversity In the recent past, a few studies systematically reviewed and mapped SCP studies and similar approaches globally [48][49][50][51].However, to our knowledge, no such assessment has been conducted specifically for the European context.Given the timeliness of EU policies and the strong legacy of SCP application across Europe, we specifically review the scientific literature to assess where and how SCP and related conservation planning approaches have been applied in a European context.We explore the properties and indicators of complexity applied in the available literature and evaluate the uptake of these studies in subsequent scientific and policy documents.By also drawing on previous reviews at a global scale, we discuss prospects, directions and gaps in conservation planning applications in Europe and highlight opportunities for more integration across objectives, models and realms, emphasizing the critical role that SCP in particular will play in reaching European conservation policy targets across scales.

Methods
We conducted a structured review of existing scientific literature, covering references that applied SCP and other related approaches in a European context (including the UK, Norway and all Balkan states in the process of joining the European Union).We purposefully excluded global studies and set our focus on articles from the European geographical context, but recognize that a rich source of the literature that has applied such approaches on other continents also exists [50].We primarily focused on literature with a conservation or restoration planning aim, including biodiversity conservation issues and gap analyses.Although the focus of the review was on SCP approaches (see search term in electronic supplementary materials), other approaches for identifying where to act or what to do were also captured.We did not specifically consider literature focusing on other fields (e.g.landscape-or urban planning), but explicitly record if and how land-use aspects have been considered in the analysed literature (table 1).To identify relevant literature, we used the Scopus search engine.We recognize that other search engines might yield slightly different results, but do not know of any systematic bias that would affect the broad scale patterns observed in this analysis.We also acknowledge other review guidelines that might increase repeatability in the future (http://prisma-statement.org/).The query was run on the 23rd of September 2022 and resulted in an initial 1459 articles for screening.A full list of the terms passed to the search engine can be found in the electronic supplementary material.
We screened the title and abstract of each of the resulting articles for suitability for inclusion in the review, and removed all studies that were broadly irrelevant, i.e. unlikely to have applied any planning approaches in a biodiversity-relevant context, or were conducted at an irrelevant extent (globally, or outside of European Member states/the European continent).This yielded a total of 356 studies across terrestrial, freshwater and marine realms, which we then assessed in more detail by extracting a set of key variables and criteria relevant for this review (table 1).Finally, we also complemented these studies with other sources of scientific literature about conservation planning beknown to the authors.This was done in order to specifically include studies that were not indexed by Scopus, making use of a 'snowballing' system, where any added known study was screened for their cited references and assessed for further literature not yet considered.
All found European studies were then assessed for their fulfilment of different criteria of planning complexity (table 1).These criteria are whether a study accounted for connectivity, considered current/future conditions and competing land-uses, and had indicated policy relevance or involved stakeholders.For each identified study in our final dataset, we extracted information on the 'uptake' in the scientific and policy literature.As a generic proxy for 'uptake', we make use of the number of citations in scientific and policy documents, realizing that this number can only give a conservative estimate of the true relevance of a work.We used the 'rscopus' package to extract this information for each article with a Digital Object Identifier [52] and here mainly relied on the PlumX citation metrics, which provide insights into by whom (social media, scientific, policy documents) and when articles are cited.See the Data accessibility section for access to the full list of studies considered.We furthermore provide an online interactive website to navigate through the outputs of the analysis (https://martin-jung. github.io/Review_EuropeanConservationPlanning).
Finally, we used the parameters extracted from the literature (table 1) and interrogated the data in terms of who cited them using a series of Bayesian regression models.In the case of citations, we used zero-inflated Poisson distributed Bayesian regression models to estimate the conditional effect of certain parameters on the relative rate of citations.We used a zero-inflated link function to account for the articles that have never been cited and furthermore included a temporal random intercept to account for year-to-year differences, given that older studies are more likely to have accumulated citations over time.Bernoulli distributed regressions were used for all other analyses, where the aim was to test for differences in the mean.Analyses were conducted using the 'brms' package [53,54].

Review findings
In total, we found 266 suitable studies covering 40 individual countries, or broader regional and European extents across the period from 1996 to 2023 (figure 1b).European studies using SCP and related approaches were mostly conducted on land (67% of all studies), followed by marine studies (20%).The most represented countries are Spain (10.7% of all studies), the UK (10%), Portugal (9.1%) and Finland (9.1%, figure 1a).Studies predominantly covered local scales (54%), with the fewest number of studies being conducted at the European scale (11.3%, figure 1b).Most studies aimed to either identify priority areas (40.3%) or investigate representation gaps and sufficiency (30%) of existing protection measures.The most applied methodological approaches were using heuristics (see also electronic supplementary material, table S1), with most of the studies using standalone software such as Marxan (31% of all studies), followed by Zonation (20%) or ranking and scoring approaches (19.7%).The remaining studies used exact algorithms such as Integer programming (19.4%); with other approaches such as multi-criteria analyses or machine learning accounting for the remaining 29.9%.Most planning studies considered multiple ecosystem types in terms of priorities for conservation areas or actions (62%).Close to half of all studies (46%) used features that only considered species in their work, ranging from 1 to over 4447 species (electronic supplementary material, figure S1), although an increasing number of studies also considered ecosystem services (10%, electronic supplementary material, figure S1) or multiple feature types together (24%).
royalsocietypublishing.org/journal/rstb Phil.Trans.R. Soc.B 379: 20230015 Interestingly, not even one of the assessed studies of European extent fulfilled all criteria for an adequate accounting of the complexities of spatial planning (table 1 and figure 2).An overwhelming proportion of studies (87%) considered only contemporary data on biodiversity, land use, climate and other factors.Similarly, most studies focused on entire landscapes (62%) instead of making specific assessments, for example, forest conservation priorities (8.3%).Only 37% of all studies accounted somehow for connectivity in the prioritization, with the most common approach being neighbourhood constraints, which penalized the selection of isolated areas for conservation.Even fewer studies considered future states of their features (12.9%), i.e. using future distributions of species or habitats, or anticipated costs.Remarkably, very few studies (11.1%) involved stakeholders in the conceptualization or execution of their study, although 68% of all studies aimed to be relevant for or to influence one or more policies.Notably, not a single conservation planning study at European scale considered the views of stakeholders (electronic supplementary material, figure S2).Conservation priorities often compete with alternative land-or water uses.Yet only 54.5% of all studies somehow accounted for these constraints, most commonly in the form of opportunity costs.
Citations of scientific and policy documents can serve as a coarse proxy of their uptake by the respective communities.On average, any given planning study was cited about 27 times (median: 17, range: 0-162) in scientific documents, 1.4 times (median: 0, range: 0-21) in policy documents and 22 times in other outreach channels such as social media, blog posts or news articles (range: 0-434).While on average, a study is cited about 2.9 times for every year after it has been published, it can take an average up to 4.4 years before a study is first cited in any policy document.We also find that that the probability that a scientific study is cited by policy documents decreases every year as increasing numbers of scientific studies are published (β = −0.05,d.f.= 261, p = 0.03).We found no correlation between the number of social media mentions and the number of citations in scientific (r = −0.06,d.f.= 261, p = 0.34) or policy documents (r = 0.02, d.f.= 261, p = 0.79).We did however find that articles that are cited more frequently by scientific documents also tended to be cited more often in policy documents (r = 0.45, d.f.= 261, p < 0.001).
The number of citations by scientific and policy documents differed according to the properties of the respective studies (figure 3).We found that studies at European extent were more often cited than comparable studies at local extent by both policy documents (l Europe = 1.7) and scientific (l Europe = 26) documents published in the same year (figure 3).While studies that accounted for aspects of connectivity (λ = 31) or land use (λ = 26) were on average cited more frequently by scientific documents than comparable studies, the best determinant of higher citation rates by policy documents was the involvement of stakeholders in the study (λ = 2.24, figure 3).Studies that considered the views of stakeholders usually had case study-specific policy objectives and were of smaller extent (figure 3).Whether or not studies have made reference to none or some of the policy contexts resulted in small differences in scientific citations (figure 3, λ none = 28, λ single = 32).However, studies that referred to a single policy context were more often cited in policy documents (λ = 2.8), although there was little difference in the uptake by scientific documents with regards to whether a study had or had not referred to any policy contexts (figure 3).Overall, these results highlight that the magnitude of uptake of SCP and related approaches differs among scientific and policy audiences with regard to study scale and complexity.

Discussion
Expansion of areas under effective conservation management is a key aspect in European biodiversity policies.However, given the limited financial resources, trade-offs between preservation of biodiversity and other competing human objectives, there is a need to    prioritize efforts.In this work, we reviewed the scientific literature on SCP and related approaches in Europe to understand where and how planning for places and actions has been applied across scales and realms.Clear patterns of predominant practices emerged, and crucially we found that not a single study accounted for all aspects of planning complexity that might be preferable in a welldesignated spatial plan of conservation priorities (table 1).Very few studies (13%) accounted for future conditions in some form, which is a large oversight given that climate change is expected to shift the distribution of most European species and habitats [38,55] and conservation management is expected to contrast projected land-use change, where it would have the highest negative impacts on biodiversity [56].Nevertheless, we show that many SCP studies, specifically those referring to specific policy contexts, are cited in policy documents, highlighting the relevance of prioritization studies as scientific evidence and decision support.Unfortunately, in Europe, which SCP studies have resulted in the designation of new spatially targeted conservation areas or improved management and restoration actions is not known or officially documented.
Implementing the EU Biodiversity strategy for 2030 requires engaging diverse stakeholders, including the general public, about how biodiversity management should be conducted within and outside protected areas [57].We find that-regardless of the method of consultation, scale or purpose of planning-stakeholder inputs are rarely considered in European planning studies (figure 2).This result aligns with the findings of global reviews of integrated land-sea planning studies, which found that most did not involve or consult stakeholders in any form [58]. Further, our results suggest that studies considering the views of stakeholders were on average more often cited by policy documents than scientific literature (figure 3d ), which could hint at a disconnect between the relevance of conservation prioritization studies for scientific outlets and policy making.Although the benefits and necessities in addressing and integrating drivers of biodiversity decline across scales and extents are well identified [59,60], is also notable that not a single study at European scales engaged with stakeholders and only a few at national or regional scales, which might further enforce the perception that conservation planning can be seen as a 'top-down' approach or 'black-box' driven by science.
Terrestrial studies by far dominated the scientific literature, whereas freshwater and cross-realm planning approaches, e.g.those that consider terrestrial as well as freshwater and/or marine systems [21,35,37], have rarely been conducted (figure 1).This constitutes a problematic issue, as there is increasing evidence that drivers behind biodiversity pressures are interlinked across realms [59].We thus amplify previous calls to step up implementations and proof-of-concept case studies of cross-realm European planning to adequately design and implement catchment plans that can contribute to jointly halting the decline of freshwater and terrestrial biodiversity [1].
Overall, 55.4% of investigated studies consider some type of socio-economic cost or constraint in their planning (figure 2).And additionally, studies that incorporated multiple objectives criteria received on average 10% more scientific citations than those studies that did not, and they make up less than half of all studies that incorporated non-biological factors into their planning exercises.This aligns with previous reviews of conservation planning studies that highlighted a general focus on biological rather than socio-economic patterns and processes [48].In a European context that can be an issue as the heterogeneity and governance of different land systems necessitate planning concepts that ideally fulfil multiple functions for nature, economy and society [14,61].Integrated planning has been highlighted as key to address the multiple drivers of biodiversity decline and to maximize synergies across policy goals and realms [1,5,6,62,63].Clearly, there is a need to further mainstream the consideration of multiple objectives in SCP, especially in working landscapes and for including nature's contributions to people.

(a) Perspective on recent advances
Our review has shown that a wide range of approaches and tools have been applied in European planning studies and among them SCP remains the best-suited approach to prioritize and evaluate potential conservation outcomes and explicitly address conflicts and trade-offs.
(i) Novel tools and ease of access SCP software continues to be developed and expanded in terms of complexity [25].Recent developments include spatially optimal zoning [43,64], next-generation ranking algorithms for spatial prioritization [65], integer programming for planning for places and actions [66][67][68], restoration of specific landscapes patterns [69] or the use of reinforcement learning for identifying conservation priorities [70] or management actions [71].Recent studies have proposed new objective functions that allow the achievement of multiple targets linearly [27,68] or by identifying more compact solutions with core areas to benefit species sensitive to edge effects [72].Each of these approaches comes with their own promises, benefits and caveats (see electronic supplementary material, table S1) and there is no tool that is universally regarded as the most appropriate by all end-users.
Nevertheless, simple scoring methods remain pervasive in planning processes across scales (figure 2), often driven by the demand of stakeholders for transparent and understandable processes.This is worrying, given that these have been known to be imprecise and potentially misleading in identifying priorities for places or actions [73].Most likely, there remains a lack of easily useable tools particularly for non-academics or those unfamiliar with developing analytical code, as well as a lack of capacity building to strengthen the skillset with existing tools.The move towards cloud-based prioritization software such as the Marxan Planning Platform (MaPP, https://marxansolutions.org/marxanmapp/) will hopefully also contribute towards reducing entry barriers for analysts with less technical training.

(ii) Towards integrated spatial planning
We highlight several methodological developments in SCP, for which we see a promise in their application in the context of spatial planning at the European extent (table 2).The integration of conservation actions within human-dominated landscapes makes conservation challenging, as any actions to restrict use and access will directly affect the users of these landscapes or displace other types of land use [86].An answer could be integrated planning solutions, that balance competing demands between preservation of royalsocietypublishing.org/journal/rstb Phil.Trans.R. Soc.B 379: 20230015 biodiversity, provision of ecosystem services and economic or cultural demands towards land and seascapes [31,62,87,88].Such applications of SCP hold great promise in identifying priorities that integrate across policy sectors (horizontal) and scales (vertical).For example, in the context of the European Biodiversity Strategy it is necessary to ensure that management for conservation is effective, especially considering limited resources, and that it ideally maximizes benefits across varying policy objectives such as biodiversity and climate mitigation and adaptation goals [55,89].
However, the data or required information are not always available for developing a spatial plan, and with greater complexity this increases the risk of incorrectly prioritizing areas or actions due to poor data or modelling assumptions [90].For example, it has been found that planning solutions are particularly sensitive to aggregated constraints, e.g.those acting at the level of a single planning unit or over the whole area of interest [91].The complex dynamics and socio-cultural factors (i.e.sense of place and ownership, land tenure) governing European working landscapes highlight the importance of considering non-biological factors in spatial plans.Yet, the critical decision of which socio-economic data are 'good enough' to include highlights issues of data harmonization and provenance.Overall, there seems an urgent need to better align social, economic and ecological objectives in spatial planning.
Similarly, most conservation planning approaches try to reduce planning complexity by using static 'proxy' variables for threats to biodiversity or level of intactness, such as aggregated 'human-footprint' indices.This lack of differentiation of separate pressures to biodiversity, and accounting for their specific impacts, impede the identification of appropriate management actions to abate these threats, and also come with the invalid assumptions that pressures have additive impacts [92].Future integrated planning studies should attempt to better account for such idiosyncrasies by proposing ways to manage different types of land-and seascapes, ideally through linkages with domain-specific data and knowledge.

(iii) Dynamics and process-based planning
To ensure that SCP is fit for purpose to tackle the complexity of conservation problems, more conceptual work on expanding and testing common problem formulations for the selection of areas is needed.Current SCP approaches do not yet comprehensively evaluate the impact of future changes or account for dynamics of natural and socio-economic systems (figure 2; electronic supplementary material, table S1).Here a better incorporation of connectivity within the problem formulation could help to identify solutions that are more robust to future changes [43,44,85].For example, the identification of adaptive dispersal corridors can help species populations to persist in the light of climate change and for future range expansion [38,93].Further, novel approaches such as reinforcement learning bring some promises, for example, for spatial planning over highly dynamic problems or policy horizons [71].At the same time, this also comes with the cost of interpretability because resulting planning solutions cannot be easily explained by analysts (typical 'black box') and the influence of data or model uncertainties cannot be comprehended.Clearly, there is a need to better understand uncertainties in parameter choices and how they influence resulting solutions and communicate them, especially towards stakeholders and less-trained analysts.(iv) Adequacy of scale-specific planning There is also an increasing realization that SCP needs to integrate across scales [60].For example, while many management problems for protected areas might only effectively be addressed at local scale (figure 1), influencing pressures such as climate change or governance regulations and constraints to national biodiversity strategies occur beyond the local scale [94].There is a need to identify practical ways forward regarding how bottom-up and top-down objectives can be integrated in spatial planning.Plausible scenarios for evaluating trade-offs, as well as a well-designed theory of change underpinning any proposed place or action-based implementation, will likely help to improve acceptance and policy impact of SCP.Supporting the implementation of SCP along all implementation steps in commonly used frameworks [37] would likely support a more effective implementation.
Moving forward, we also recommend that evidence and results from SCP studies should be more readily accessible across different scales and realms, and some such efforts have been spearheaded elsewhere in Gabon or globally [17,50,95].One idea could be to build a European-wide reference database highlighting different SCP frameworks, case-studies and tools, by also providing the evidence behind these works (e.g.data, maps and indicators used for evaluation) in a transparent and digestible way.Similar databases already exist in the context of the European Marine Spatial Planning directive (Directive 2014/89/EU, https://maritime-spatial-planning.ec.europa.eu/msp-practice/database),but not for either terrestrial or freshwater systems.A European hub of SCP frameworks and evidence could help to improve cohesiveness and consciousness for conservation issues, particularly for cross-border or cross-realm challenges, and may contribute to a widespread adoption of SCP.

Conclusion
Our review on the current state of SCP in European contexts highlights the varying levels of complexity-or lack thereof-in how conservation decisions are determined.In a mission-driven discipline like conservation, scholarly work should strive to be useful and close to implementation.Policy relevance can be achieved through addressing many of the complexity factors outlined above, such as the following: (a) by incorporating stakeholder visions and preferences in SCP.The fact that stakeholders are rarely consulted in scientifically oriented SCP studies might hint at one of the symptoms explaining why protected areas are often of low efficiency, particularly if conflicting objectives and initial 'buy-in' by stakeholders are ignored; (b) by more comprehensively integrating multiple objectives and the socio-economic aspects that matter.Spatial plans for conservation in European multi-functional landscapes cannot be realized without considering the trade-offs with such management actions; (c) by considering robust policy contexts and targets for the biodiversity attributes that matter, rather than 'proxy' variables with little prospect of implementation or actionable advice; (d) by expanding and developing the set of openly available data and tools and providing decision makers with capacity-building opportunities and training to expand the use of SCP as standard.
SCP can contribute more than just maps.It can estimate the sufficiency of management plans, identify synergies and trade-offs or evaluate different planning scenarios in terms of their benefits.Addressing current and future conservation challenges can only happen through widespread adoption of best practices and use of evidence, with scientists and practitioners jointly contributing to this process in a concerted way.We thus urge European scientists to thus make further efforts to increase the relevance of their planning work.

Figure 1 .
Figure 1.Spatial and temporal patterns of conservation planning studies in Europe.Shown are the spatial distribution (a), the temporal trend of studies separated by spatial extent (b), and the number of studies by realm (c).

Figure 2 .
Figure 2. Overview of the properties of the studies identified in the review.Shown are factors related to connectivity, whether a study accounted for land use, and if the study aimed at a particular policy objective and whether stakeholders have been involved in any capacity in the conceptualization of the study.The bottom axes separate between levels of these factors related to the study aim.The sizes of the points indicate the numbers of studies, while the colours show the proportions of all studies for the study aim (bottom axes).

Figure 3 .
Figure 3.The results of a Bayesian regression model assessing the difference in the number of citations in policy or scientific literature, or the probability of stakeholder involvement, differ depending on certain properties of the reviewed studies.

Table 1 .
Depiction of variables, types, and the rationale behind the collection in the review.
'contemporary', we refer to any dataset collected prior to the conducted analysis.Future or dynamic planning approaches usually include or consider variables or constraints beyond the 2030 period.Analysis would consider both the contemporary state and future conditions (e.g.future climatic refugia).purpose of planning type (single categorical term).Broad categorization of the goal of the planning exercise, being for instance identification of priority areas for management implementation (e.g.placement of protected areas, usage zones, restoration), specific actions (e.g.eradication of invasive species), or representation (e.g.coverage of features) or identification of synergistic effects (e.g.minimization of costs across objectives).policy relevance name of relevant policies or 'none'; in the case of a specific concrete case-study, enter 'case study' Whether the work is explicitly trying to address objectives of a policy as opposed to being curiosity-or methodologically-driven (e.g.demonstration of a new method using a particular EU case study).algorithm approach method Listing the tool or approach used for planning, i.e.Marxan biodiversity type species | ecosystems | Nature Contributions to People (NCP) | other What types of biodiversity data were considered in the work and at what level was it included.royalsocietypublishing.org/journal/rstb Phil.Trans.R. Soc.B 379: 20230015

Table 2 .
Recent conceptual and methodological innovations and developments in SCP, with exemplary studies for their application.